CHICAGO (Reuters) - A U.S. congresswoman urged the Labor Department on Monday to investigate Chipotle Mexican Grill for possible wage theft, another potential hurdle for the burrito chain as it seeks to rebound from food-safety problems last year.

U.S. Representative Rosa DeLauro, a Democrat from Connecticut, said the department should probe allegations from about 10,000 current and former Chipotle employees who have joined a federal lawsuit that alleges the company did not properly pay them for hours worked.

Such actions, if true, would contradict federal law, DeLauro said in a letter to the department, "depriving workers of the wages and earnings to which they are legally entitled."

Chipotle said her call for an investigation was "misdirected."

"We have maintained from the outset that this case is without merit and will vigorously defend our employment practices," company spokesman Chris Arnold said.

The Labor Department had no immediate comment.

Chipotle has been working to revive sales growth after outbreaks of E. coli, norovirus and salmonella linked to its restaurants sickened more than 500 people last year and drove away customers.

Last week, activist investor William Ackman disclosed that his hedge fund had purchased a 9.9 percent stake in the company, saying it was undervalued.

The case over unpaid wages began two years ago when Leah Turner, who worked as a manager at a Chipotle restaurant in Colorado, alleged in a lawsuit that the company routinely required hourly paid employees to work "off the clock," according to court records.

The company used timekeeping devices that automatically punched employees off the clock, even if they were still working, the lawsuit said.

Since then, about 10,000 others from across the country have joined the lawsuit seeking to recover unpaid wages, said Andrew Quisenberry, an attorney representing the workers for law firm Bachus & Schanker. The large number of plaintiffs is "significant to us, showing that it's widespread across Chipotle," Quisenberry said.

The case is Tuner et al vs Chipotle Mexican Grill, U.S. District Court, District of Colorado, No. 14-cv-02612.